For several medical therapy situations it is necessary to expose a lesion of some sort to radiation in order to be able to remedy the problem.
As an example, traditionally a stenosed coronary artery is often treated by balloon dilatation, i.e. Percutaneous Transluminal Coronary Angioplasty (PTCA). A small balloon at the top of a plastic catheter is inserted into the femoral artery, guided in the vessels to the site of the stenosis, and inflated. As the stenosis is pushed out by the balloon, the artery is widened to normal inner diameter. In order to further improve the treatment, a so called stent is mostly positioned at the location of the stenosis. However, in about one third of the patients, a restenosis will still occur after the PTCA was performed.
One means of reducing the restenosis rate is to treat the vessel wall locally with X-ray, gamma or beta radiation in conjunction with the PTCA. The exact mechanism by which radiation inhibits restenosis is not yet fully understood. However, a radiation dose amounting to about 10-50 Gy from catheterised gamma and beta (radiation) sources have been shown to lower the restenosis rate substantially in several trials.
Conventionally, radioactive sources, e.g. in the form of radioactive nuclides have been used to supply the required radiation. In cases where a lesion has varying extensions and thicknesses in different directions inside a vessel, it can be very difficult to provide a radiation dose tailored to the lesion at hand. The prior art methods and devices are based on the provision of a plurality of radioactive isotopes (nuclides), arranged in a row, as disclosed in e.g. U.S. Pat. No. 5,899,882 (Novoste Corp.). The major disadvantage with this method is that the length cannot, or at least only with difficulty can, be adapted to the actual case. If, for example, an irradiation device provided with isotopes over a length of 4 mm, is used to irradiate a lesion of 3 mm length, it goes without saying that healthy tissue will be undesirably exposed to radiation.
In order to achieve a rotationally symmetric and uniform irradiation, various mechanical methods and means have been used in the prior art. These prior art means are provided for the centering of the radiation source in a vessel mechanically, e.g. by suitable spacer means.
In contrast to radioactive sources, e.g. in the form of said radioactive nuclides, in applicants"" U.S. patent application Ser. No. 08/805,296 (corresponding to WO 98/36796), incorporated herein, in its entirety, by reference, there is disclosed a miniaturized source of ionizing electromagnetic radiation, comprising a pair of plates; a hermetically sealed microcavity formed in one of the plates; a pair of electrodes in the form of a cathode and an anode, at least one electrode being located in the microcavity and the other electrode being located on the other plate; the anode being at least partly of a metal having a relatively high atomic weight; and electrically conducting leads connected to the cathode and the anode. Furthermore, in applicants"" U.S. provisional application 60/137,478 (corresponding to Swedish patent application no. 9902118-0) there is also suggested an X-ray source that is possible to switch on and off electronically.
Another device is based on a balloon catheter for dilatation, but where the balloon is filled with radioactive liquid through the catheter lumen. This device has a disadvantage in that there is a risk that radioactive liquid inadvertently could come out into the surroundings.
Still another approach is to cover the balloon of a balloon catheter device with a radioactive coating.
As touched upon already, a problem that the prior art devices suffer from is the difficulty of controlling the dosage delivered, in spatial terms. I.e. in view of the fact that the individual radiation sources in U.S. Pat. No. 5,899,882 (Novoste) essentially are point sources, in order to cover a larger area, there must be provided a plurality of point sources on a guide wire. This could be difficult from a manufacturing point of view, and also the assembly of several X-ray source will be relatively bulky if a large number of radiation sources are provided, and this could cause difficulties in the manipulation of the guide wire e.g. inside the narrow coronary vessels.
Also, it may be crucial to deliver an exact amount of radiation, in that too much radiation kills cells, and too little radiation may cause cancers and other cell growth without actually achieving the desired treatment effect.
Thus an object of the present invention is to provide a device for delivering ionizing radiation (e.g. X-rays) to a therapy location, wherein the control of the dosage over the selected therapy region can be significantly improved. In particular the treated lesion should be subjected to a known and controlled radiation dose. Healthy tissue should not be subjected to significant radiation doses. By xe2x80x9ccontrolledxe2x80x9d is meant that the tissue will be subjected to a known amount of radiation at a given depth, regardless of the thickness of the lesion.
In order to solve the problem, the invention provides means for enabling the manipulation of a radiation source so as to change its position at the therapy location in order to control the dose in terms of the amount of radiation delivered and in terms of where it is delivered. Especially it enables the adjustment of its position in the longitudinal direction in a vessel, when radiation is to be provided over a larger area than is covered by the radiation lobe from an individual radiation source. Furthermore, the invention provides for the rotation of the source inside a vessel.
The object indicated above is achieved with a device as claimed in claim 1.
In a further aspect the invention concerns a method of providing a controlled dose of ionizing radiation to a lesion at a therapy location, the method being defined in claim 10.
Embodiments specifically addressing various problems are defined in the dependent claims.